Scientific Forecaster Discussion
fxus66 kmfr 220537
Area forecast discussion
National Weather Service Medford or
1035 PM PDT Sat Oct 21 2017
Updated aviation discussion.
Update...current radar and satellite imagery are showing light
showers across southern Oregon and northern California with a
heavier swath of rain to our north. The cold front to our north is
still on track to drift southward tomorrow, but it should continue
to weaken leading to light to moderate rain west of the Cascades
and the Siskiyous northward.
The Wind Advisory is currently set to expire at 11pm tonight, but
will be making a few changes to the wind forecast tonight to
account for the latest guidance for east of the Cascades. Will
need to consider extending the Wind Advisory for a few more hours.
Otherwise, no changes to the forecast have been made. -Schaaf
Aviation...22/06z taf cycle...a mix of MVFR and VFR ceilings and
visibility (and isolated IFR conditions) continues tonight in moist
onshore flow ahead of another front, and this general condition is
expected to continue through Sunday (especially for areas west of
the cascades). South to southwest winds will remain gusty through
Sunday morning at the coast, over the higher terrain, and east of
the Cascades, diminishing some Sunday afternoon. Mountain
obscuration will continue to affect most of the forecast area
We have introduced some lower visibility and ceilings Sunday evening
for mfr based on the high soil moisture and increasing stability
leading to the chance for some fog/mist and IFR conditions. These
conditions will likely affect more valley locations later Sunday
Previous discussion... /issued 202 PM PDT Sat Oct 21 2017/
Short term...tonight through Tuesday night...current radar
imagery depicts a wide swath of rain just to our north, with
widespread showers streaming west to east across the forecast
area. These will gradually taper off through the rest of the day.
The warm front responsible for the rain, as well as the rapid
increase in snow levels, has moved to the north, but a weak cold
front will attempt to push back south later tonight and through
tomorrow. This front will wash out as it moves south, and while
another round of light to moderate precipitation will accompany
it's passage through the day, it won't fully make it across the
forecast area. In fact, most locations east of the Cascades and
south of the Siskiyous won't see much rain, if any at all.
The clouds and showers will exit the region Sunday night, and high
pressure will start building in for the first half of the week.
This will result in drying and warming conditions, as well as
prevailing easterly winds in the lower levels. With the moisture
now in the ground and cooler temperatures settled in, this east
wind is likely to create strong overnight inversions, trapping air
within the valleys and limiting the mixing with the drier air
aloft. Fog will be a concern both Monday and Tuesday morning in
the west side valleys, but fog is possible east of the Cascades as
well, especially Monday morning. If fog forms, it will limit the
daytime highs significantly, but if it does not, unseasonably warm
temperatures of 5 to 10 degrees above normal are not out of the
question for much of the region.
Also of note, a Chetco effect is a likely byproduct of these east
winds, and temperatures along the southern coastline near
Brookings could approach 80 by Tuesday afternoon. This warmth is
expected to persist into the extended period. -Bpn
Long term...Wednesday through Saturday...confidence is high
we'll remain dry during the period. The models show an upper
trough dropping southeast from western b.C. Through northeast
Washington on Wednesday. Typically the trajectory that the models
show do not result in precipitation. The more likely scenario will
be a dry cold front passage that will result in cooler
temperatures. The models have backed off on the quantitative precipitation forecast Wednesday with
the GFS showing northing in our area. The European model (ecmwf) still shows some,
but suspect it's overdone. Given the above mentioned reasoning,
pops have been removed from the forecast Wednesday and Wednesday
night. Dry with milder temperatures are expected next Thursday and
could last into next weekend. Skies will be clear for the most
part at night, so it will be cool west of the Cascades and colder
on the Eastside.
Marine...updated 130 PM PDT Saturday 21 October 2017...a warm
front has moved north of the area, and gale force south winds are
now diminishing over portions of the waters. Seas will remain
steep to very steep through Sunday afternoon as west swell
combines with short period wind waves. A cold front will move
onshore Sunday. Once the front moves inland, a thermal trough will
set up, and this will bring strong north winds and steep seas
south of Cape Blanco beginning Monday and continuing through
Fire weather...updated 200 PM PDT Saturday October 21 2017...no
fire concerns are expected through the weekend. Confidence is high
for a stretch of dry weather starting next Monday and could last
through next weekend. Guidance continues to show a tight pressure
gradient as a thermal trough develops along the coast Monday night
through Tuesday. This could result in moderate northeast winds along
with moderate overnight recoveries near and at the ridges.
or...Wind Advisory until 11 PM PDT this evening for orz030-031.
California...Wind Advisory until 11 PM PDT this evening for caz085.
Pacific coastal waters...Small Craft Advisory until 5 PM PDT Sunday
for pzz350-356-376. Small Craft Advisory for hazardous seas
from 5 PM Sunday to 5 PM PDT Monday for pzz350-356-370-376.
Hazardous seas warning until 5 PM PDT Sunday for pzz350-356-